The major problem in reducing the size of the higher power mobile radios and high power continuous duty base stations are the size requirements for the RF power amplifier heatsink. The size of the heatsink is inversely proportional to the efficiency for the RF power amplifier. That is, the higher the efficiency of the RF power amplifier, the smaller the size of the heatsink. At "peak" efficiency of the RF power amplifier, the heatsink is small. However, broadband RF power amplifiers never operate at "peak" efficiency over all operating conditions. The RF power amplifier would have to be tuned for the varying operation conditions of fundamental frequency, supply voltage, temperature, output power an actual antenna impedance. To operate at "peak" efficiency all of the time, the RF power amplifier would have to have the capability to tune itself as operation conditions vary.
Attempts have been made to improve the efficiency of RF power amplifiers. These methods have incorporated the use of active output matching networks and harmonic wave shaping. In U.S. Pat. No. 4,439,741 and other similar designs, a switching network, responsive to the operating conditions of the RF power amplifier, is used to switch to an alternate output matching network of the RF power amplifier. Accordingly, a need exists for RF power amplifiers that will operate at "peak" efficiency over all operating conditions, resulting in the reduction of the size of the heatsink.